Written by

James Dean
| FLORIDA TODAY

SpaceX has the cheapest plan for developing a commercial space taxi, while The Boeing Co. has the strongest technical approach, according to a NASA evaluation of their proposals.

Sierra Nevada Corp.'s mini-shuttle offers a promising alternative to the two capsules but must overcome the most technical challenges, NASA determined.

In a 13-page report released recently, the agency explained why it awarded those three firms up to $1.1 billion to complete designs of private rockets and spacecraft that could fly astronauts to the International Space Station by 2017. ...